1. Field of the Invention
The present invention relates to a process for the processing of pyrolysis gasoline. More particularly the invention relates to a separation of the pyrolysis gasoline into commercially attractive fractions and treating the fractions to remove or convert unwanted contaminants. More particularly the invention relates to an integrated process wherein the separations are carried out concurrently with a specific treatment in distillation column reactors containing the appropriate catalysts.
2. Related Art
Pyrolysis gasoline is a gasoline boiling range (.about.97-450.degree. F.) petroleum stock obtained as a product or by-product from a process in which thermal processing is used to crack a petroleum stock. One example is the destructive cracking of a naphtha boiling range material to produce ethylene. Another example is the delayed coking of a residual petroleum stock to produce lighter components, including coker gasoline.
Products from these thermal cracking processes contain high concentrations of olefinic materials as well as saturated (alkanes) materials and polyunsaturated materials (diolefins). Additionally, these components may be any of the various isomers of the compounds. In addition the gasoline boiling range material contains considerable amounts of aromatic compounds.
The pyrolysis gasolines are typically processed to removed unwanted acetylenes, diolefins and sulfur compounds. Some of the diolefins may be recovered, especially isoprene.
The C.sub.5 's are recovered and are useful in isomerization, etherification and alkylation. As noted above, isoprene is also recovered as a useful product. Normally, however, the diolefins are removed along with acetylenes by selective hydrogenation. If desired the C.sub.5 's may be completely hydrogenated and returned to the naphtha cracker ethylene plant as recycle.
The C.sub.6 and heavier fractions contain sulfur compounds which are usually removed by hydrodesulfurization. The aromatic compounds are often removed and purified by distillation to produce benzene, toluene and xylenes. The aromatic containing fraction is often treated with clay material to remove olefinic material.
Finally the heavy boiling gasoline is normally treated by caustic treating to remove the mercaptans and olefins prior to being used as a gasoline blending stock. In the present refinery scheme many of the separate steps and processes of the prior art are combined into single multifunctional catalytic distillation columns.